The present invention is directed to a system and method for detecting pain and its components using magnetic resonance spectroscopy (MRS).
Chronic pain is a major problem in our health care. The assessment of chronic pain is, however, limited by its subjective nature and the inability of any current diagnostic technique to objectively quantify any changes associated with the presence of pain per se.
Chronic pain has an enormous impact both in terms of individual suffering and economic impact through use of health care resources and reduced ability to engage in work and other activities and treatment. However, the assessment of pain and the subsequent use of treatment is largely based on subjective report by the patient.
Chronic pain is one of the most common and yet difficult to treat of conditions. It has traditionally been regarded merely as a symptom of pathology. This concept has served well in an acute pain model where treatment is directed at treating pathology and when there is resolution of pain with subsequent healing. However the model has not worked well in the chronic pain situation. In this situation, ongoing pathology, as in arthritis or nerve injury, may give rise to ongoing pain and may not be treatable with currently available remedies. Even more difficult, in many situations there is ongoing pain with no identifiable pathology that may be the cause for persistent pain. In these situations particularly psychological factors may be invoked as an explanation for ongoing pain that is resistant to treatment. Although it is now recognized that a psychological origin for pain, i.e., hysteria or malingering, is uncommon, it is also recognized that psychological factors have an important role in the presentation of any pain. Pain has three distinct but overlapping components: nociceptive, neuropathic and psychological. All of these may contribute in varying degrees to a person's perception and expression of pain.
Nociceptive pain is the most common type of pain and is believed due to signals arising from pathology in body tissues. Thus, appendicitis, kidney stones and joint inflammation in arthritis all give rise to increased inputs from the structures affected and this is perceived as pain. Although there may be modification of these inputs (either up or down) by physiological processes in the brain and spinal cord, basically pain is due to increased inputs arriving in the central nervous system. A subject usually responds to treatments that reduce these inputs such as nerve blockade, analgesics, anti-inflammatories or psychological treatments that increase levels of inhibition and thereby reduce inputs.
In distinction to nociceptive pain, the second pain component, neuropathic pain, occurs as a result of damage to the peripheral or central nervous system. In its strictest definition, this type of pain occurs in the presence of features of neurological dysfunction such as sensory or motor deficits. It has different features and is often described as shooting, electric, burning or shock-like. It may be difficult to detect pathology with current imaging techniques. It generally responds poorly to the strategies used for the treatment of nociceptive pain such as analgesics, anti-inflammatories and nerve blockade or even section. This type of pain responds better to strategies that reduce inputs due to nerve damage such as discharges arising from neuromas or to drugs that increase the level of inhibition in the central nervous system.
The third pain component, the psychological component, is a universal contribution to our experience of pain. Psychological processes can influence both pain perception and pain expression (disability) in an upward or downward reaction. For example, during a sports match, many athletes will not notice or disregard a sometimes severe injury so that both pain and disability are minimal in the face of quite large inputs from damaged structures. Conversely, mood changes such as anxiety or depression or learned processes such as fear-avoidance may enhance both the perception of pain and associated disability.
Although it is widely recognized that these processes are at work in people with pain, it is currently extremely difficult to determine the relative contribution of each of these three pain components to a person's presentation. This is despite the fact that many of the treatments currently available depend on accurate diagnosis of the type of pain present. As mentioned, the treatments for nociceptive and neuropathic pain are quite different and have little value when used for the wrong conditions. Psychological treatments can be used for both types of pain. However, current psychological treatments are directed more towards addressing disability and the ability to cope with pain than with changing pain perception itself. However, in some people in whom negative psychological processes are active, recognition of this would help direct treatment towards addressing these issues rather than a search for a nociceptive or neuropathic focus that may be relatively minor.
Thus, the best treatment for pain depends on a accurate assessment of the different components that contribute towards someone's sensation of pain. Current diagnostic techniques are unreliable and give limited information. Many diagnostic techniques are unable to accurately identify sources that may be giving rise to nociceptive or neuropathic pain. Even if damage to an intervertebral disc or nerve root, for example, can be demonstrated, it is extremely difficult to determine with any confidence that even this structural abnormality is giving rise to pain. It is also difficult to determine the relative contribution of psychological factors. Although there are a number of tests that can assess pain perception, mood, motor disability and cognitions, it is still difficult to determine to what extent these changes are contributing to a person's pain presentation.
There is therefore a huge need for a system and method that can objectively and accurately assess the relative contributions of each of the components to a person's pain. Current instruments are largely reliant on subjective self report. An objective method of reliably detecting changes associated with pain perception would enhance both the assessment and treatment of pain. If the techniques could also assess the relative contributions of the different pain components (nonciceptive, neuropathic and psychological), this would revolutionize pain medicine.
One study has reported that low back pain is associated with a decrease in glucose in the frontal cortex as well as an increase in glucose in the thalamus. (Grachev, I. D., Fredrickson, B. E., and Apkarian, A. V. Abnormal brain chemistry in chronic back pain: an in vivo proton magnetic resonance spectroscopy study. Pain 89:7-18, 2000). This article is incorporated by reference herein.
Another study reported biochemical changes in several brain regions in a small number of subjects with low back pain and pain following spinal cord injury. (Pattany, P. M., et al., Proton magnetic resonance spectroscopy of the thalamus in patients with chronic neuropathic pain after spinal cord injury, Am. J. Neuroradiol., 23:901-905, 2002). This article is incorporated by reference herein.
However, there is currently no objective means of detecting the components or types of pain.